Discoloration (known as “blueing”) is caused by tuning characteristics, cam timing, carburetor jetting, overheating, etc. This is not caused by a manufacturer defect. Biker’s Choice® offers products that will help prevent or remove discoloration. Reference our Chemical section. For any bikes with modified or performance exhaust systems, we recommend a High Performance Air Filter and a Fuel Controller for fuel injected bikes, or Jet Kits and/or Carburetors in our Fuel & Air section for carbureted bikes. This is for increased satisfaction in power, fuel mileage and “rideability”. Use of any modified exhaust may not meet Federal EPA emissions and noise standards.ied exhaust may not meet Federal EPA emissions and noise standards.